Failure Analysis of Retrieved UHMWPE Tibial Insert in Total Knee Replacement

This study involves the failure analysis of an ultra high molecular polyethylene (UHMWPE) tibial insert from Apollo (R) Total Knee System, which was removed after 10 years of service from an 70 years old female patient. The tibial insert was investigated by using a stereoscope, scanning electron microscope (SEM), infinite focus microscope (IFM) and energy disperse spectroscopy (EDS) to characterize the morphology and composition of the bearing surface. Differential scanning calorimetry (DSC) and Fourier transform spectroscopy (FTIR) were employed to characterize the degradation and crystallinity of the component. Gel-permeation chromatography (GPC) was used to measure the polyethylene tibial insert molecular weight. Results showed that the failure of total knee replacement (TKR) was associated with high grade wear with oxidation degradation. Surface delamination, scratch marks, pitting, folding, and embedded third body particles were observed on the retrieved UHMWPE tibial surface. The damage features observed on the UHMWPE tibial insert suggested degradation is due to fatigue related wear and oxidative-induced. From the depth measurement of the pit, the depths are large as 35 mu m and 60 mu m. Overall results showed that the UHMWPE tibial insert which retrieved from the patient who is an active and not overweight have a decreases in material properties and high grade wear that can contribute to the failure of the tibial insert after 10 years used.